1. Field
The present embodiments relate to a liquid crystal display device, and a driving method thereof.
2. Related Art
Flat panel display devices have been used as a visual information transmission medium. The cathode ray tube or Braun tubes, which were conventionally used as the visual transmission medium, are heavy and large in size. Generally, the flat panel display device is lighter and smaller in size than the conventional cathode ray tube.
For example, flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electro luminescence (EL). Most of these display devices have been put to practical use and used on the market.
The liquid crystal display device has rapidly replaced with the cathode ray tube in many application fields. As electronic products are being produced that are lighter, thinner, shorter and smaller the demand for a display device with these characteristics has also increased. Thus, the liquid crystal display device has become popular because of the smaller and lighter design and the improved mass-productivity of the liquid crystal display device.
An active matrix type liquid crystal display device drives a liquid crystal cell by use of a thin film transistor (hereinafter, referred to as ‘TFT’). An active matrix type liquid crystal display device has excellent picture quality and the power consumption is low. Because of the popularity of the liquid crystal display device a large amount of development has went into the product. The liquid crystal display device has high resolution is capable of being mass produced.
FIGS. 1 and 2 represent an active matrix type liquid crystal display device and a drive signal thereof according to the related art.
Referring to FIGS. 1 and 2, the active matrix type liquid crystal display device includes a liquid crystal display panel 13 where m×n number of liquid crystal cells Clc are arranged in a matrix type. M number of data lines D1 to Dm cross n number of gate lines G1 to Gn. A TFT is formed at the crossing part thereof. A data drive circuit 11 supplies data to the data lines D1 to Dm of the liquid crystal display panel 13. A gate drive circuit 12 supplies a scan pulse to the gate lines G1 to Gn.
The liquid crystal display panel 13 contains liquid crystal molecules between two glass substrates. The data lines D1 to Dm and the gate lines G1 to Gn formed on a lower glass substrate of the liquid crystal display panel 13 cross each other perpendicularly. The TFT formed at the crossing part of the data line D1 to Dm and the gate line G1 to Gn supplies a data voltage, which is supplied through the data line D1 to Dn, to the liquid crystal cell Clc in response to the scan pulse from the gate line G1 to Gn. A source electrode of the TFT is connected to a pixel electrode of the liquid crystal cell Clc. A black matrix, a color filter and a common electrode (not shown) are formed on an upper glass substrate of the liquid crystal display panel 13.
A polarizer where the optical axes are at right angles to each other is stuck onto the upper glass substrate and the lower glass substrate of the liquid crystal display panel 13. An alignment film for setting a pre-tilt angle of liquid crystal is formed on the inner surface being in contact with the liquid crystal.
A storage capacitor Cst is formed in each of the liquid crystal cells Clc of the liquid crystal display panel 13. The storage capacitor Cst is formed between a pre-stage gate line and a pixel electrode of the liquid crystal cell Clc or formed between a common electrode line (not shown) and the pixel electrode of the liquid crystal cell Clc, so as to fixedly maintain a voltage of the liquid crystal cell Clc.
The data drive circuit 11 is composed of a plurality of data drive IC's of which each includes a shift register, a latch, a digital-analog converter and an output buffer. The data drive circuit 11 latches the digital video data and converts the digital video data into an analog gamma compensation voltage to supply to the data lines D1 to Dm.
The gate drive circuit 12 is composed of a plurality of gate drive IC's of which each includes a shift register that sequentially shifts a start pulse for each one horizontal period to generate a scan pulse. A level shifter converts an output signal from the shift register into a signal of a suitable swing width for driving the liquid crystal cell Clc. An output buffer connected between the level shifter and the gate line G1 to Gn. The gate drive circuit 12 sequentially supplies the scan pulse to the gate lines G1 to Gn to select a horizontal line of the liquid crystal display panel 13 to which the data are to be supplied.
In FIG. 2, ‘Vd’ is a data voltage that is outputted by the data drive circuit 11 to be supplied to the data lines D1 to Dm, and ‘Vlc’ is a data voltage that is charged or discharged in the liquid crystal cell Clc. ‘Scp’ is a scan pulse that is generated for one horizontal period. ‘Vcom’ is a common voltage supplied to the common electrode of the liquid crystal cells Clc.
The liquid crystal display device has a high cost because a lot of data lines D1 to Dm are formed in the liquid crystal display panel 13 and because of the drive IC's of the data drive circuit 11 that supply the data voltage to the data lines D1 to Dm. The cost increases as the resolution gets higher or the liquid crystal display panel 13 is made larger.
In order to solve the problem caused by the increase of the data lines and the data drive IC's, two liquid crystal cell rows are driven with one data line so as to develop the technique of reducing the number of the data lines and the number of the drive IC's, as shown in FIG. 3. The liquid crystal display device of FIG. 3 connects the TFT for driving different liquid crystal cells from each other to the left and the right of the data lines D1, D2, D3 in a pixel array. The data lines D1, D2, D3 time-dividedly drives two liquid crystal cells disposed on the left and the right thereof by sequentially applying the scan pulse synchronized with the data to the two gate lines for each ½ horizontal period, thereby reducing the number of the data lines.
The liquid crystal display device as in FIG. 3 can reduce the number of data lines, but the TFT's connected to the left and the right of the data line increases the load of the data line.
Accordingly, a liquid crystal display device that reduces the number of data drive IC's and the load of a data line is desired.